I'm a Nikoli addict, I'll admit it. (See my other reviews of the Nikoli ____ & Sudoku books). I bought all of their US-released books, subscribe to their puzzle site, and have even had books shipped from Japan. What I like about these books in particular is the size and binding. These things matter to a puzzle addict. The spiral binding allows you to hold the book more easily, and the book is made with high-quality thick paper (not newsprint like many crossword books). That means you can solve in pen (if you dare!) and not have it show through to the other side, or you can erase without worrying about the paper abrading or ripping. These half-sudoku books are kind of a shame (we Americans have PLENTY of sudoku to choose from), and I wish it had more of the "new" puzzle type.
Nurikabe is one of Nikoli's classic number puzzles. Each number you see tells you how many white squares must be that room. Black squares are used to separate rooms, but must all connect orthogonally (in north/south east/west directions). The harder the puzzle, the more you have to rely on advanced logic. I won't spoil the fun of figuring these tactics out! Buy this book and enjoy - just beware - you'll go through lots of pencil-sharpening (or mechanical clicking) to do these on paper, since you're shading in entire boxes (rather than drawing lines or writing numbers, as in other Nikoli puzzle types).